1. Field of the Invention
The present invention relates to a catadioptric optical system which is suitable for enlarging a sample (object) for observations, and an image pickup apparatus having the same.
2. Description of the Related Art
In the present pathological examination, a pathological sample is directly observed with a human eye using an optical microscope. In recent years, a so-called virtual microscope is used, which captures a pathological sample as image data and enables it to be observed on a display. Since the virtual microscope enables the image data of the pathological sample to be observed on the display, a plurality of people can observe it at the same time. Moreover, this virtual microscope has many advantages: For example a diagnosis can be requested by sharing the image data with a distant pathologist. A traditional virtual microscope, however, needs a long time to take an image of a pathological sample and to capture its image data.
One time-consuming factor is a narrow image-pickup area of a microscope used to capture a wide image-pickup range of a pathological sample as image data. It is necessary for the narrow image-pickup area of the microscope to take images multiple times or through scanning and to synthesize them into one image. Therefore, an (image-pickup) optical system having a wide image-pickup area is required in order to make the number of shots smaller and to make an image capturing time period shorter.
Along with the wide image-pickup area, an optical system having a high resolution in a visible range (wide wavelength region) is also required. The optical system having a high resolution is required not only for use in pathological diagnosis but also for various fields.
Japanese Patent Publication No. S60-034737 discloses an objective lens of a microscope which includes a dioptric optical system that reduces aberrations well in the entire visible light range, and is suitable for observing a biologic cell or anything.
Japanese Domestic Publication No. 2007-514179 discloses an ultra-broadband ultraviolet microscope video system having a high resolution in an ultraviolet wide wavelength range using a catadioptric imaging optical system to detect defects in an integrated circuit or a photomask. WO00/039623 discloses a catadioptric optical system which is suitable for manufacturing a semiconductor device and configured to expose micro patterns on a wide area.
The objective lens of the microscope disclosed in Japanese Patent Publication No. S60-034737 reduces aberrations well in the entire visible light range, but the size of the observation area is not sufficient. Moreover, the broadband microscope catadioptric imaging optical system disclosed in Japanese Domestic Publication No. 2007-514179 reduces aberrations well in a wide wavelength range and provides a high resolution, but the size of the field of view is not sufficient.
The catadioptric imaging optical system disclosed in WO00/039623 provides a high resolution over a wide range, but a wavelength region where aberrations are corrected well may not have a sufficient width. A microscope lens for enlarging a sample for observations is demanded to have a large observation region and high optical performance in a wide wavelength range.